rebase destroys branches

Hello,
          I am evaluating git for use in a company. Please correct if I am wrong. I am concerned that an inexperienced developer could mistakenly rebase branches, destroying the original branch. Attached is a script (Windoze) that shows the 'topic' branch being moved!, after the rebase we are unable to see the original branch, read it's history or find it's commit points.

Surely no operation should remove anything from the repository. Operations like this irreversibly break the repository . When rebasing the original branch must be retained.

Yours faithfully,

Gene Thomas.

From: "Gene Thomas [DATACOM]" <Gene.Thomas@datacom.co.nz>
Sent: Monday, March 04, 2013 11:06 PM

The original branch is not 'destroyed', rather the pointer to the previous tip is within the logs. All the content is still available until the logs expire.

It's easy to misread some of Git's strengths if you have come from other historic corporate 'version control systems' which are often based on drawing office practice of old (e.g. the belief there is a single master to be protected is one misconception for software).

Rebase, at the personal level, is an important mechanism for staff to prepare better code and commit messages. Trying to hide the reality will just make your management 'control' less effective as staff work around it and delay check-ins, etc.

The broader access control and repo management issues are deliberately not part of Git, and there are good tools for that. e.g. Gitolite.

Philip

Philip,
        Thanks for your reply.

Is that the 'git log' log or internal logs? Are you sure? There doesn't appear to be a way to checkout that tip of see the log back from that tip.

So we will be unable to checkout content after a time?

Gene Thomas.

-----Original Message-----
From: Philip Oakley [mailto:philipoakley@iee.org] 
Sent: Tuesday, 5 March 2013 12:44
To: Gene Thomas [DATACOM]; Git List
Subject: Re: rebase destroys branches

From: "Gene Thomas [DATACOM]" <Gene.Thomas@datacom.co.nz>
Sent: Monday, March 04, 2013 11:06 PM

The original branch is not 'destroyed', rather the pointer to the previous tip is within the logs. All the content is still available until the logs expire.

It's easy to misread some of Git's strengths if you have come from other historic corporate 'version control systems' which are often based on drawing office practice of old (e.g. the belief there is a single master to be protected is one misconception for software).

Rebase, at the personal level, is an important mechanism for staff to prepare better code and commit messages. Trying to hide the reality will just make your management 'control' less effective as staff work around it and delay check-ins, etc.

The broader access control and repo management issues are deliberately not part of Git, and there are good tools for that. e.g. Gitolite.

Philip

On Tue, Mar 05, 2013 at 02:05:32PM +1300, Gene Thomas [DATACOM] wrote:

See the dovcumentation for "git reflog"

You need to make a distinction between a user's local repository, and the team's central repository. The workflow of the individual user is one where they can and should be allowed to use rebase and "git commit --amend" if they like. Consider this the same thing as the user who chooses to use "quilt" on their local machine while they are preparing their patches, so they are carefully honed before they are cast into concrete. Whether they use "quilt", or manual patching, or simply don't bother checking things into the central SCM until things are cleaned up, the end result is the same.

The team's central repository is one where you don't want to allow history to be lost, and so there you can enforce rules to prevent this. For example, if you use Gerrit, you can limit the ability to reset branches to administrators only. Everyone else can only add new commits, not change older ones.

(If someone accidentally checks in NDA'ed material belonging to someone else, or some other IP content guaranteed to cause your general counsel to have heart palpitations, trust me, you'll want to allow administrators to rewind a git branch. :-)

You can also use Gerrit to enforce code reviews, so that no change goes in until a second engineer reviews the commit and gives it a thumbs up (with a permanent record of the code review kept in Gerrit, something which can be important for pointy-haired corporate types who worry about Sarbanes Oxley controls --- although from your e-mail address, you may be lucky enough to be exempt from needing to worry about SOX controls :-).

Regards,

						- Ted

From: "Gene Thomas [DATACOM]" <Gene.Thomas@datacom.co.nz>
Sent: Tuesday, March 05, 2013 1:05 AM

Double checking the [rebase] manual page... [The ref] "ORIG_HEAD is set to point at the tip of the branch before the reset."

So your original branch starts there (I just checked one of mine). Obviously this is only for the machine that did the rebase, and only has the last rebase tip. But then until it's pushed to an open repo no one knows ;-)